Single Global Positioning System Research Articles

Testing Patch, Helix and Vertical Dipole GPS Antennas with without Choke Ring Frame

Abstract: The antenna is the connecting part between Global Positioning System (GPS) satellite and receiver, and it works on transferring the satellite signal propagation to the receiver with minimum interruption. This is beside the main role that GPS antenna can play for accurate and precise positioning. High quality GPS antennas have high gain, systematic radiation pattern, Right Hand Circular Polarization (RHCP), and low directivity. Multipath error is a principal error source connected with GPS positioning and it can be mitigated using better antenna design. GPS antennas tend to be provided with choke ring frame for protection from the reflected RHCP electromagnetic waves. In this paper, the performance of three different types of GPS antenna, namely: Microstrip Patch Antenna (MPA), Helix antenna (HA), and Vertical Dipole antenna (VDA), with and without choke ring frame, has been investigated using single frequency GPS receiver. The antennas have been examined under the same GPS environment, including satellites constellation, geometry, and surroundings, with different heights from the ground reflector surface for multipath evaluation. Short base-line kinematic differential code GPS (DGPS) technique has been used for removing and mitigating the main GPS error sources and focusing on multipath effect. Satellite residuals and the quality of the obtained positioning have been considered for evaluating the performance of each antenna. The results have reflected the ability of choke ring frames to improve the performance of the three GPS antennas with different rates in multipath areas, and illustrate the advantages and limitations of each antenna. Keywords: Micro-strip, Patch, Helix, Vertical Dipole, GPS, Choke Ring Antenna, Multipath.

The Advantages and Limitations of Low-Cost Single Frequency GPS/MEMS-Based INS Integration

Global Positioning System (GPS) provides a method for directly obtaining instantaneous position and velocity estimates using satellites-based passive range measurements. GPS is a whole day, all-weather, passive, satellite positioning system. Inertial Navigation System (INS) is a navigation aid system that uses a computer and Inertial Measurement Unite (IMU). IMU includes motion sensors and rotation sensors to continuously calculate relative position, orientation, and velocity. The integration of GPS/INS can help to overcome the limitations of the two systems providing integrated system better than either on a stand-alone basis. The integration of low-cost INS with dual frequency GPS has been widely studied and the same for the integration of tactical grid INS with low-cost GPS. However, during the last a few years, a number of low-cost GPS\low-cost INS integrated systems have been introduced and become popular in various engineering applications. However, reliable investigations into the advantages, limitations and quality of such integration level are still needed and more efforts are required, which will be the focus of this paper. The methodology followed in this paper for evaluating the integration of low-cost GPS/INS sensors depends on evaluating the two sensors individually and comparing the results with the integrated system. The results show that low-cost single frequency GPS receivers are able to provide a comparable accuracy level in both static and kinematic carrier phase differential GPS (DGPS). As for low-cost Micro-Electro-Mechanical System (MEMS)-based IMU, the accelerometers have provided instability comparing to gyros. The performance of gyros can be improved based on modelling the nearly-linear behaviour of the gyro drift. Tests show that the integration of low-cost GPS sensors with MEMS-based INS degrades the quality of gyro measurements and may not add any improvements to the quality of the individual GPS positioning.

Improved 2D Ground Target Tracking in GPS-Based Passive Radar Scenarios.

Global Positioning System (GPS) satellites offer promising opportunity for Passive Radar systems due to their global coverage and the availability of multiple satellites throughout the world. However, their low power at ground level limits system coverage. In this paper, a GPS based Passive Radar which exploits a single illumination source, and uses digital array processing for ground targets localization is presented. To face signal power problems, a processing scheme combining reconstructed reference signals, adaptive filtering techniques and spatial filtering is implemented. Conventional beamforming techniques are used to increase the level of the target echo before the detection stage, and high resolution DoA estimation techniques are applied to estimate targets azimuth. Ground target localization in local Cartesian space is performed taking into account the system geometry, range and azimuth information. Both synthetic and real radar data are used to analyse system operation. During the measurement campaign, a cooperative vehicle was used for validation purposes. Results confirm that ground targets detection and localization are feasible using a single GPS transmitter.

Ionospheric Disturbances Observed From a Single GPS Station in Hong Kong During the Passage of Super Typhoon Hato in 2017

AbstractThe powerful convection in the lower atmosphere, for example, tropical cyclones (TCs), has a high probability of causing ionospheric disturbances. We observed evident ionospheric disturbances during the passage of Super Typhoon Hato in 2017 by analyzing the highest elevation vertical total electron content (HeVTEC) time series, that is, the VTEC from the Global Positioning System (GPS) satellite with the highest elevation at each epoch, retrieved from a single GPS station in Hong Kong. The results demonstrate that the daily maximum of HeVTEC time series on each day during the TC period experienced a large fluctuation ranging from 33.5 TEC unit (TECU) to the peak value 62.0 TECU. The peak value 62.0 TECU occurred on the TC landfall day 23 August 2017, approximately twice as high as that of non‐TC‐impacted days. We also found that the TEC spatial gradients above the landfall area increased by around 50% and 200% in the north‐to‐south and west‐to‐east directions, respectively. We also examined the daily mean bias (MB) of VTEC above Hong Kong with respect to the mean VTEC during the past 27 days from 20 July to 15 August in 2017. The largest VTEC MB was observed in the west of the landfall area along the TC moving direction, on the TC landfall day. Our findings provided the evidence that the Hato's landfall over the coast near Hong Kong caused the apparent ionospheric disturbances above the landfall area.

Estimation of the ocean tide loading displacements by GPS and GLONASS kinematic Precise Point Positioning

Ocean Tide Loading Displacement (OTLD) parameters, derived by Global Positioning System (GPS) approach, need more time to converge to a stable state and show poor precision of K1 and K2 constituents. Combining multi-system Global Navigation Satellite System (GNSS) data can greatly improve the positioning accuracy and significantly reduce the convergence time compared to single GPS PPP, combined GPS+GLONASS with ambiguity resolved in kinematic Precise Point Positioning (PPP) is improved on the basis of the algorithm of GPS kinematic PPP. We collected eight years of continuous observations of 11 worldwide sites from International GNSS Service to generate three dimensional OTLD parameters of eight constituents using GPS with ambiguity fixed, GLONASS with ambiguity free and combined GPS+GLONASS with ambiguity fixed kinematic PPP approach. The results show the eight constituents derived by GPS_FX and GPS+GLONASS_FX solution need four years and three years to converge to stable values, respectively. GLONASS can significantly improve the convergence rate of K1 and K2 constituents which needs only two years to converge to stable values, and S2 and P1 constituents which need three years to stable values. The results also show the GPS+GLONASS/reference misfits are the smallest for the most constituents in three components (less than 2mm) except for K2 and K1 in vertical and north directions. GLONASS can improve more than 40% in vertical and north components over GPS and GPS+GLONASS for K2 and K1 constituents and show very close agreement with GPS_FX solution in vertical and north component for S2 and P1 constituents. Ambiguity resolved in OTLD estimation can significantly accelerate the convergence and improve the accuracy for eight constituents, especially for combined GPS+GLONASS kinematic PPP mode, but no single constellation mode solution for all eight major constituents exists.

Tropospheric Refractivity Profile Estimation by GNSS Measurement at China Big-Triangle Points

Atmospheric radio refractivity has an obvious influence on the signal transmission path and communication group delay effect. The uncertainty of water vapor distribution is the main reason for the large error of tropospheric refractive index modeling. According to the distribution and characteristics of water vapor pressure, temperature, and pressure, which are the basic components of the refractive index, a method for retrieving atmospheric refractivity profile based on GNSS (Global Navigation Satellite System) and meteorological sensor measurement is introduced and investigated in this study. The variation of the correlation between zenith wet delay and water vapor pressure is investigated and analyzed in detail. The partial pressure profiles of water vapor are retrieved with relevance vector machine method based on tropospheric zenith wet delay calculated by single ground-based GPS (Global Positioning System) receiver. The atmospheric temperature and pressure is calculated with the least square method, which is used to fit the coefficients of the polynomial model based on a large number of historical meteorological radiosonde data of local stations. By combining the water vapor pressure profile retrieving from single ground-based GPS and temperature and pressure profile from reference model, the refractivity profile can be obtained, which is compared to radiosonde measurements. The comparison results show that results of the proposed method are consistent with the results of radiosonde. By using over ten years’ (through 2008 to 2017) historical radiosonde meteorological data of different months at China Big-Triangle Points, i.e., Qingdao, Sanya, Kashi, and Jiamusi radiosonde stations, tropospheric radio refractivity profiles are retrieved and modeled. The comparison results present that the accuracies of refractivity profile of the proposed method at Qingdao, Sanya, Kashi, and Jiamusi are about 5.48, 5.63, 3.58, and 3.78 N-unit, respectively, and the annual average relative RMSE of refractivity at these stations are about 1.66, 1.53, 1.49, and 1.23%, respectively.

Inferring the Horizontal Speed of an Ionospheric Irregularity From a Single GPS Scintillation Receiver at High Latitudes

AbstractWe propose a new technique to infer the horizontal speed of ionospheric irregularity at high latitudes from the refractive components of the global positioning system (GPS) L1 (1575.42 MHz) and L2 (1227.60 MHz) carrier phases using only a single ground‐based receiver that can log measurements at 50–100 Hz. The test data at Jang Bogo Station (geographic: 74.6°S and 164.2°E; geomagnetic: 77.2°S) in Antarctica and at Sachs Harbor (geographic: 71.9°N and 234.7°E; geomagnetic: 75.6°N) in the Arctic were analyzed for a one‐year period in 2019. The results were compared with data from ground‐based radar observations, the Vertical Incidence Pulsed Ionospheric Radar (VIPIR) in Antarctica and the Canadian Advanced Digital Ionosonde (CADI) in the Arctic, which measures the ion drift velocity at the apex. Although it is difficult to directly compare GPS and radar measurements due to the steep gradient of fast plasma motion in narrow regions at high latitudes, the probability density of the ionospheric irregularity speeds from the two different instruments were consistent with the correlation coefficients of 0.81 and 0.85 in the Southern and Northern hemispheres.

Pass-by-Pass Ambiguity Resolution in Single GPS Receiver PPP Using Observations for Two Sequential Days: An Exploratory Study

“Pass-by-pass” or “track-to-track” ambiguity resolution removes Global Navigation Satellite System (GNSS) satellite hardware delays between adjacent undifferenced (UD) ambiguities, which is often applied in precise orbit determination (POD) for Low Earth Orbit (LEO) satellites to improve the accuracy of orbits. In this study, we carried out an exploratory study to use the “pass-by-pass” ambiguity resolution by differencing the undifferenced ambiguity candidates for two adjacent passes in sidereal days for a single Global Positioning System (GPS) receiver static Precise Point Positioning (PPP). Using the GPS observations from 132 globally distributed reference stations of International GPS Service (IGS), we find that 99.08% wide-lane (WL) and 97.83% narrow-lane (NL) double-difference ambiguities formed by the “pass-by-pass” method for all stations can be fixed to their nearest integers within absolute fractional residuals of 0.2 cycles. These proportions are higher than the corresponding values of network solution with multiple receivers with 97.39% and 91.20%, respectively. About 97% to 98% of ambiguities can be fixed finally on average. The comparison of the estimated station coordinates with the IGS weekly solutions reveals that the Root Mean Square (RMS) in East and North directions are 2-4 mm and is about 6 mm in the Up direction. For hourly data, it is found that the mean positioning accuracy improvement can achieve to about 10% after ambiguity resolution. From a dam deformation monitoring application, it shows that the fixing rate of WL and NL ambiguity can be closed to 100% and higher than 90%, respectively. The time series generated by PPP are also in agreement with the short baseline solutions.

An Integrated Navigation Method Based on an Adaptive Federal Kalman Filter for a Rice Transplanter

HighlightsAn integrated GPS/INS/VNS navigation system was developed to improve navigation accuracy.An adaptive federal Kalman filter with information distribution factors was used to fuse navigation information.Detection of seedling row lines was achieved based on subregional feature points clustering.A modified rice transplanter was developed as an experimental platform for automatic navigation.Abstract. In this article, an integrated global positioning system (GPS), inertial navigation system (INS), and visual navigation system (VNS) navigation method based on an adaptive federal Kalman filter (KF) is presented to improve positioning accuracy for a rice transplanter operating in a paddy field. The proposed method used GPS/VNS to aid the INS and reduce the influence of the accumulated error of the INS on navigation accuracy. An adaptive federal KF algorithm was designed to fuse navigation information from different sensors. The information distribution factor of each local filter was obtained adaptively on the basis of its own error covariance matrix. Computer simulation and transplanter tests were conducted to verify the proposed method. Results showed that the proposed method provided accurate and reliable navigation information outputs and achieved better navigation performance compared with single GPS navigation and an integrated method based on a conventional federal KF. Keywords: Federal Kalman filter, GPS/INS/VNS, Information distribution factor, Information fusion, Integrated navigation.

Accessorial Locating for Internet of Vehicles Based on DOA Estimation in Industrial Transportation

With the improvement of living standard and the development of science and technology, Internet of Vehicle (IOV) will play an important part in industrial transportation as a main research field of Internet of Things. As a result, it is very necessary to grasp the location of vehicle. However, the traditional single global position system is easily affected by the external environment, so an accessorial locating approach based on wideband direction of arrival (DOA) estimation in intelligent transportation is proposed. First, model the array received signal on the road infrastructure. Then, by means of random forest regression (RFR) in the supervised learning, upper triangle elements of the covariance matrix of each frequency and the actual DOA are, respectively, extracted as the input features and output parameters; thus, the corresponding prediction coefficients are solved by training. After that, the trained RFR model can be used to calculate the final direction using test samples. Finally, these vehicles can be located according to the geometrical relation between the vehicle and the infrastructure. The proposed algorithm is not only suitable for uncorrelated signals but also for uncorrelated and correlated mixed signals without wideband focusing. The simulations show that compared with some sparse recovery algorithm, the prediction accuracy and resolution are effectively improved.

Analysis of the Beidou navigation satellite system: Interoperability and performance

Based on the new trends and requirements introduced by the development of the international navigation satellite systems from the single global positioning system (GPS) era to the multiple global navigation satellite system (GNSS) era, the Beidou-3 navigation satellite system (BDS-3) has been designed to ensure compatibility and interoperability with other GNSS systems based on four features, i.e., constellation, signal, time, and coordinate. In terms of constellation design, the BDS-3 constellation orbit altitude and inclination design consider the constellation complementary requirements with the GPS, GLONASS, and Galileo systems. Thus, the PDOP of GNSS improves by 37.9% on average. BDS has acquired interoperability with respect to the signal structure; therefore, it is in agreement with other systems using a similar frequency and spectrum. Thus, users can simultaneously use the navigation services of each major system without changing the hardware design. In terms of time and coordinate, BDS has realized a reference system that is considerably consistent with the systems used on an international scale, resulting in a time difference offset of 50 ns with international UTC and GLNT, which is consistent with the international ITRF 2014 coordinate parameter accuracy. Thus, BDS-3 has achieved interoperability with other GNSSs based on the four aforementioned aspects and can provide better service to global users in combination with other GNSSs.

Athlete Workloads During Collegiate Women's Soccer Practice: Implications for Return to Play

Athlete monitoring via wearable technology is often used in soccer athletes. Although researchers have tracked global outcomes across soccer seasons, little information exists on athlete loads during individual practice drills. Understanding these demands is important for athletic trainers in making decisions about return to play. To provide descriptive information on total distance, total player load (PL), total distance per minute, and PL per minute for practice drill structures and game play by player position among female soccer athletes across a competitive season. Retrospective observational study. National Collegiate Athletic Association Division I university. A total of 32 female collegiate soccer players (age = 20 ± 1 years, height = 168.75 ± 4.28 cm). Athletes wore a single global positioning system and triaxial accelerometer unit during all practices and games in a single soccer season. Individual practice drills were labeled by the team's strength and conditioning coach and binned into physical, technical and tactical skills and large- and small-sided competition drill structures. Descriptive analyses were used to assess the median total distance, total PL, total distance per minute, and PL per minute by drill structure and player position (defender, forward or striker, and midfielder) during practices and games. Large- and small-sided competition drills imposed the greatest percentage of workload across all measures for each position (approximately 20% of total practice), followed by physical drills. When comparing technical and tactical skills drills, we found that technical skills drills required athletes to cover a greater distance (approximately 17% for technical skills and 15% for tactical skills), and tactical skills drills required higher play intensity during practices across all positions (approximately 18% for technical skills and 13% for tactical skills). Defenders had the highest median PL outcomes of all positions during practices. Different practice drill types imposed various levels of demands, which simulated game play, on female soccer athletes. Athletic trainers and other clinicians may use this information in formulating objective return-to-play guidelines for injured collegiate women's soccer players.

Real‐time detection of BDS orbit manoeuvres based on the combination of GPS and BDS observations

The construction of the third generation of the Chinese BeiDou navigation satellite system (BDS), which provides global positioning, navigation, and timing (PNT) services, will be completed in 2020. As BDS satellites contain the geostationary orbit (GEO), inclined geosynchronous (IGSO), and medium earth orbit (MEO), orbital manoeuvres occur more frequently. Thus, orbit manoeuvre detection is important for continuous and reliable PNT services. A BDS orbit manoeuvre detection method based on the combination of global positioning system (GPS) and BDS observations is proposed in this study. The standard deviations of the observation residuals of the epoch-differenced velocity estimation of the single BDS system and combined GPS + BDS system were compared to determine the beginning and end of the orbit manoeuvre. The results show that the orbital manoeuvre leads to a position, velocity, and receiver clock error bias of approximately tens to hundreds of metres, several centimetres per second, and tens to hundreds of metres, respectively. Based on the proposed method, the start and end times can be detected in real time and the usable observation time can be extended by >157 min.

GPS/BDS RTK Positioning Based on Equivalence Principle Using Multiple Reference Stations

Reliable real-time kinematic (RTK) is crucially important for emerging global navigation satellite systems (GNSSs) applications, such as drones and unmanned vehicles. The performance of conventional single baseline RTK (SBRTK) with one reference station degrades greatly in dense, urban environments, due to signal blockage and multipath error. The increasing use of multiple reference stations for kinematic positioning can improve RTK positioning accuracy and availability in urban areas. This paper proposes a new algorithm for multi-baseline RTK (MBRTK) positioning based on the equivalence principle. The advantages of the solution are to keep observation independent and increase the redundancy to estimate the unknown parameters. The equivalent double-differenced (DD) observation equations for multiple reference stations are firstly developed through the equivalent transform. A modified Kalman filter with parameter constraints is proposed, as well as a partial ambiguity resolution (PAR) strategy is developed to determine an ambiguity subset. Finally, the static and kinematic experiments are carried out to validate the proposed algorithm. The results demonstrate that, compared with single global positioning system (GPS) and Beidou navigation system (BDS) RTK positioning, the GPS/BDS positioning for MBRTK can enhance the positioning accuracy with improvement by approximately (45%, 35%, and 27%) and (12%, 6%, and 19%) in the North (N), East (E), and Up (U) components, as well as the availability with improvement by about 33% and 10%, respectively. Moreover, the MBRTK model with two and three reference receivers can significantly increase the redundancy and provide smaller ambiguity dilution of precision (ADOP) values. Compared with the scheme-one and scheme-two for SBRTK, the MBRTK with multiple reference receivers have a positioning accuracy improvement by about (9%, 0%, and 6%) and (9%, 16%, and 16%) in N, E, and U components, as well as the availability improvement by approximately 10%. Therefore, compared with the conventional SBRTK, the MBRTK can enhance the strength of the kinematic positioning model as well as improve the positioning accuracy and availability.

Concurrent Measurement of Global Positioning System and Event-Based Physical Activity Data: A Methodological Framework for Integration

Objective: Global positioning system (GPS) data can add context to physical activity data and have previously been integrated with epoch-based physical activity data. The current study aimed to develop a framework for integrating GPS data and event-based physical activity data (suitable for assessing patterns of behavior). Methods: A convenience data set of concurrent GPS (AMOD) and physical activity (activPAL) data were collected from 69 adults. The GPS data were (semi)regularly sampled every 5 s. The physical activity data output was presented as walking events, which are continuous periods of walking with a time-stamped start time and duration (to nearest 0.1 s). The GPS outcome measures and the potential correspondence of their timing with walking events were identified and a framework was developed describing data integration for each combination of GPS outcome and walking event correspondence. Results: The GPS outcome measures were categorized as those deriving from a single GPS point (e.g., location) or from the difference between successive GPS points (e.g., distance), and could be categorical, scale, or rate outcomes. Walking events were categorized as having zero (13% of walking events, 3% of walking duration), or one or more (52% of walking events, 75% of walking duration) GPS points occurring during the event. Additionally, some walking events did not have GPS points suitably close to allow calculation of outcome measures (31% of walking events, 22% of walking duration). The framework required different integration approaches for each GPS outcome type, and walking events containing zero or more than one GPS points.

New Strategy for Improving the Accuracy of Aircraft Positioning Based on GPS SPP Solution.

The paper describes and presents a new calculation strategy for the determination of the aircraft’s resultant position using the GPS (Global Positioning System) SPP (Single Point Positioning) code method. The paper developed a concept of using the weighted average model with the use of measuring weights to improve the quality of determination of the coordinates and accuracy of GPS SPP positioning. In this research, measurement weights were used as a function of the number of GPS satellites being tracked, and geometric PDOP (Position Dilution of Precision) coefficient. The calculations were made using navigation data recorded by two independent GPS receivers: Thales Mobile Mapper and Topcon HiPerPro. On the basis of the obtained results, it was found that the RMS (Root Mean Square) accuracy of positioning for XYZ geocentric coordinates was better than 1.2% to 33.7% for the weighted average method compared to a single GPS SPP solution. The proposed approach is therefore of practical application in air navigation to improve the quality of aircraft positioning.

Is A Smartphone App A Valid And Reliable Method To Measure Bicycling Behavior?

PURPOSE: To determine the criterion validity and test-retest reliability of a smartphone app in measuring bicycling behavior. METHODS: A GPS device was used as the gold standard for comparison to the smartphone app. Courses ~2 miles in length at two locations were tested; 1) urban college campus and 2) rural bicycle path. Adult bicyclists (N=50; 21 urban, 29 rural) carried a Global Positioning System (GPS) device and their smartphone while riding a bicycle on a course loop twice (5 minute break in between); both the GPS device and smartphone app recorded location data. Movement time was recorded for the GPS device and the smartphone app, and MET*min were calculated for bicycling assuming 6 METs/min. Using a geographic information system (GIS), a 36-foot buffer was created around the road network for each course. Location data from the GPS and smartphone devices were mapped over the course buffers in GIS, and the percent of location data within the buffers was calculated for each. Validity and reliability of the percent within buffer and validity of MET*min for each device were examined using paired sample t-tests. RESULTS: GPS device data fell within the urban course buffer 69% of the time and within the rural course 37% of the time, while data from the smartphone app was within the urban course buffer 78% of the time and within the rural course 51% of the time. For the GPS device, maximum distance of a single GPS point away from the road buffer averaged 14 meters (range 0-290), while maximum distance of a single GPS point from the smartphone app averaged 15 meters (range 0-92). Mean difference between the GPS and smartphone devices was 9% in favor of the smartphone app on the urban course (n=40, p<0.05), and 13% in favor of the smartphone app on the rural course (n=54, p<0.01). For reliability of the GPS device, mean difference between the two repeated rides was 4% on the urban course (n=20, p>0.05), and 9% on the rural course (n=28, p<0.01). For reliability of the smartphone app, mean difference between the two repeated rides was 3% on the urban course (n=21, p>0.05), and 0.6% on the rural course (n=28, p>0.05). MET*min from the GPS device was 1.22 versus 1.21 from the smartphone app (n=94, p>0.05). CONCLUSIONS: The smartphone app tested is a reasonable alternative to GPS devices in assessing bicycling behavior in urban and rural environments.

Determination of NavIC differential code biases using GPS and NavIC observations

Delay bias between the pseudo range code is called Differential Code Bias (DCB), this is one of the main error sources to estimate the precise Total Electron Content (TEC) in ionosphere. Differential delay biases between the dual frequency band signals in both satellite and receiver are called satellite differential code biases (SDCBs) and receiver differential code biases (RDCBs). The combined satellite and receiver DCBs lead to measure error TEC. SDCBs and RDCBs should be removed from the Global Navigation Satellite System (GNSS) measurements accurately. The DCB estimations of GNSS signals are important for improving GNSS user positioning accuracy in ionospheric and space weather applications. The Navigation with Indian Constellation (NavIC) system has been developed by India to cater to positioning, navigation, timing, and ionosphere and troposphere remote sensing applications. The proposed DCB estimation algorithm is necessary to calibrate the NavIC TEC measurements for both NavIC satellites and receivers. In this work, a Global Positioning System (GPS)-aided NavIC DCB estimation algorithm has been implemented with the help of single station GPS TEC measurements. TEC data were recorded at the same location by the NavIC as well as the GPS receiver (Koneru Lakshamaiah Education Foundation, Guntur, India, 16.47°N, 80.61°E) for the month of September 2016. The SDCB and RDCB estimations for NavIC satellites and receivers located at Guntur, India. The maximum SDCB value of 9.2 TECU was observed for NavIC satellite pseudo range number (PRN) 3. Standard deviations of NavIC satellites were in the range of 0.53–1.11 TECU. The NavIC RDCB was estimated to be 16 TECU. The DCB results were validated with the Fitted Receiver Bias (FRB) method. The implemented DCB estimation algorithm would be useful for improving positional accuracy of NavIC users.

Low Latitude Ionosphere Error Correction Algorithms for Global Navigation Satellite System

The ionospheric errors occur due to loss of data in ionospheric region. Low latitudinal regions are the most affected regions due to ionospheric errors and also causes loss of signal or data for space based augmentation system(SBAS) such as aircraft. So to reduce these ionospheric errors in low latitude regions of Global Navigation Satellite System(GNSS) Klobuchar algorithm is used which mitigates the errors occurring in low latitude regions and is used as a standard algorithm in US Global Positioning System(GPS) till now; however, this model can reduce the ionospheric error by approximately 50-60% Root Mean Square(RMS) error in low-latitudes. So in order to increase the percentage deviation of errors in low-latitude regions, Enhanced Klobuchar algorithm is proposed which enhances the correction of low-latitude ionospheric errors approximately up to 80% RMS for a single frequency GPS user. In this paper error correction algorithms are performed over International GPS Service(IGS) data was collected using Hyderabad station receiver, Telangana (latitude- 17.41728°, longitude-78.55088°) in southern part of India during year 2016.

An unmanned aerial vehicle-aided node localization using an efficient multilayer perceptron neural network in wireless sensor networks

Localization of sensor node is decisive for many localization-based scenarios of wireless sensor networks (WSNs). Node localization using fixed terrestrial anchor nodes (ANs) equipped with global positioning system (GPS) modules suffers from high deployment cost and poor localization accuracy, because the terrestrial AN propagates signals to the unknown nodes (UNs) through unreliable ground-to-ground channel. However, the ANs deployed in unmanned aerial vehicles (UAVs) with a single GPS module communicate over reliable air-to-ground channel, where almost clear line-of-sight path exists. Thus, the localization accuracy and deployment cost are better with aerial anchors than terrestrial anchors. However, still the nonlinear distortions imposed in propagation channel limit the performance of classical RSSI and least square localization schemes. So, the neural network (NN) models can become good alternative for node localization under such nonlinear conditions as they can do complex nonlinear mapping between input and output. Since the multilayer perceptron (MLP) is a robust tool in the assembly of NNs, MLP-based localization scheme is proposed for UN localization in UAV-aided WSNs. The detailed simulation analysis provided in this paper prefers the MLP localization scheme as they exhibit improved localization accuracy and deployment cost.